1. Field of the Invention
The present invention relates to an IR cut filter that cuts IR light traveling toward a solid-state imaging element, a method for manufacturing an IR cut filter, and a solid-state imaging device.
2. Description Related to the Prior Art
A solid-state imaging device comprises a taking lens, a solid-state imaging element disposed behind the taking lens, a circuit board on which the solid-state imaging element is mounted. The solid-state imaging device is incorporated in an electronic device such as a digital camera, a mobile phone with a camera, a smartphone, or the like. The solid-state imaging element is an image sensor of a CCD-type, a CMOS type, or the like. The solid-state imaging element photoelectrically converts light incident on a light receiving surface to output three color signals. The three color signals are subjected to signal processing in a signal processing circuit incorporated in the electronic device, and then converted into image data. A taken image is displayed on a monitor based on the image data.
The sensitivity of the solid-state imaging element to the near-infrared region is higher than that of a human eye. In the case where the whole light including the IR (infrared) light is incident on the solid-state imaging element and photoelectrically converted, an image of a subject seen with human eyes and a taken image differ in color balance. For example, a green object appears as a gray or a reddish brown object and a blue-violet object appears as a reddish-violet object in the taken image.
In a solid-state imaging device described in US 2012/0257075 A1 (corresponding to JP 2012-222546 A), an IR cut filter, which cuts the infrared light while transmitting visible light, is provided between a taking lens and a solid-state imaging element to prevent the infrared light from entering the solid-state imaging element. Thereby, the color balance seen with the human eyes is reproduced in a taken image.
In the solid-state imaging device, harmful rays are caused by repetitive reflection and refraction of the visible light. Upon incidence on the solid-state imaging element, the harmful rays may cause so-called flare that is light fogging, resulting in degradation of image quality. In the US 2012/0257075 A1, the IR cut filter cuts the infrared light, but the harmful rays pass through the IR cut filter. The harmful rays are incident on the slid-state imaging element, causing the flare and also a phenomenon called “ghost” which is a clear appearance of the harmful rays in an image.